Flameholder for ram jet engine



Oct. 18, 1955 G. L. FRANCOIS 2,720,754

FLAMEHOLDER FOR RAM JET ENGINE Filed Sept. 29, 1950 INVENTOR. GUY L F RANQOIS BY 62/14, 7' @A/LYW;

ATTORNEY United States Patent Ofiice 2,720,754 Patented Oct. 18, 1955 FLAMEHOLDER FOR RAM JET ENGINE Guy Leon Francois, Ferguson, Mo.', assignor to McDonnell Aircraft Corporation, St. Louis, Mo., a corporation of Maryland Application September 29, 1950, Serial N 0. 187,411

7 Claims. (Cl. 6039.72)

This invention relates to jet engines and is more particularly directed to an improved flameholder for an ejector or ram jet engine.

The primary object of the invention is to provide a flameholder for a jet engine that will furnish more stable combustion.

Another object of the invention is to provide a flameholder that will supply a primary and a secondary air stream to a jet engine.

The invention consists in the provision of a flameholder for an ejector or ram jet engine comprising an axial member and a truncated hollow cone spaced therefrom, swirl vanes being connected therebetween, the swirl vanes creating a form of swirling reverse flow of burning gas in the unburned gas which improves the combustion of fuel introduced into the engine.

In the drawing:

Fig. 1 is a longitudinal sectional view of an ejector jet engine embodying the invention,

Fig. 2 is a perspective view of the flameholder,

Fig. 3 is a side elevational view of the flameholder; and

Fig. 4 is a view showing the flameholder embodied in a ram jet engine.

The invention is embodied in the several views of the drawing in which the numeral 1 designates the casing of a jet engine whose forward end 2 is formed to a good aerodynamic shape and adapted to fit snugly about the air inlet tube 3. This tube extends into the casing 1 and is flared outwardly to form diffuser 4. A flameholder 5 is installed in the casing just aft of the diffuser and the exhaust end of the casing is contracted to form a discharge nozzle 6. The tube 3 and the flameholder 5 are secured to the inner wall of the casing 1, preferably by welding.

The flameholder includes an inner member which is made up of a forward inner open-ended frusto-conical portion 7, a rear frusto-conical portion 8 and a cylindrical portion 7' being connected between these two frustoconical portions. An outer member comprises a hollow or annular frusto-conical portion 9 provided with a cylindrical flange 10 radially spaced from the cylindrical portion 7, the outer portion of the frusto-conical portion 9 being provided with securing members 11 for supporting the flameholder in the casing. Disposed between the cylindrical portion 7 and the cylindrical flange 10 is a plurality of swirl vanes 12 the plane of which is disposed transversely to the axis of the cylindrical flange 10. The vanes 12 are suitably secured to both cylindrical portion 7 and flange 10.

Fuel is supplied to the engine from nozzle 13 derived from a suitable source of supply and discharged therefrom under high pressure, a pump not shown being provided for this purpose. A spark plug 14 is provided for initially igniting the fuel during the starting operation of the engine. After being discharged from nozzle 13, fuel enters the inlet tube 3 and is mixed with the air therein.

When the air and fuel mixture reaches the diffuser, it

expands which introduces turbulence for mixing and a reduction in velocity. Some of the fuel and air mixture passes into the combustion chamber 15 in casing 1 about swirl vanes 12. This is regarded as primary air fuel mixture stream 26 and, by reason of the action of the swirl vanes thereon, a turbulent rotary or swirling action is set up. A secondary air fuel mixture stream 25 is supplied to the combustion chamber 15 from the space between the frusto-conical portion 9 and the interior of the casing, the fuel therein being ignited by the spark plug 14, with the resulting flame held just aft of portion 9 which functions as a flameholder. A third air fuel mixture stream 27 is created through the cones 7 and 8. The fuel and air mixture which is acted on by the vanes 12, is thoroughly mixed and ignited by a flame held just aft of the portion 8. Immediately to the rear of conic portion 7 is a small or pilot combustion chamber composed of the cylindrical portion followed by the rear conic portion 8, the gas being ignited in the pilot combustion chamber by the flame held at the rear and inside of conic portion 8 also ignites the fuel in the primary air.

The secondary air fuel stream is mixed with fuel ignited by the flame immediately aft of the primary flame held on the edges of the conic portion 9. The turbulence and reduction in the velocity of flow that is imposed on the primary air improves the mixing of the ignited fuel with the fuel in the secondary air fuel stream which action shortens the length of the burning chamber, stabilizes the flame, and causes the flame held on the flameholder to more readily ignite the fuel present in the primary and secondary air.

The flameholder 5 has the advantage that it controls the flow as well as the mixing of fuel and air, so that the velocity of the several streams of fuel and air is cut down due to the volume of the space for the fuel and air in the combustion zone immediately aft of the conic portions 7, 8 and 9. The conic portions, thus, create a turbulent condition for thoroughly mixing the fuel and air, and maintain the flame in the pilot combustion chamber and just aft of the trailing margins of conic portions 8 and 9. The pilot combustion chamber has two stages of expansion with a greater retarding effect on the velocity of the stream 27 and consequent greater flame stability for maintaining combustion of the primary and secondary streams 26 and 25.

Fig. 4 shows the flameholder assembled in a casing 16 of a ram jet engine having a forward end 17 formed to a suitable aerodynamic shape and defining an inlet nozzle 24. The rear end of this casing is shaped to form a discharge nozzle 28. A diffuser 19 is disposed in the forward end of the casing and the flameholder 5 is assembled therein in the same manner as in the ejector jet engine above described.

Fuel is supplied to the engine through conduit 20 which branches olf at 21 to discharge fuel through suitable nozzles inside of annular holder 9. Branch 22 discharges fuel into the cylindrical portion 7' connecting frusto-conical portions 7 and 8. A spark plug 23 is mounted in said connecting portion for initially igniting fuel. The flameholder operates in a ram jet engine in the same manner as in the ejector jet above described. The swirling action of the air about vanes 12 and in the trailing edge of the flameholder 9, mixes the secondary air with the fuel and the primary air, thereby increasing the combustion efliciency of the engine. The same air stream operations are employed in the modified structure illustrated in Fig. 1.

What I claim is:

l. A jet engine comprising an elongated tubular member, an air-fuel mixture flow tube secured in one end of said tubular member, a diffuser secured to said tube and to said member, a hollow outwardly flared flameholder v ,chaniber, a flameholder? between said diffuser fand -com- Lbustion'phamberprovided witlian outer member haying a frusto-c'onical portionifor Idirec'ting secondary combus- .tion airlinto said combustion chamberpast said diffuser .'and for creatingturbulence immediately. aftlof saidfrhsto- [conical porltion, said fiameholdr beingprovided-with an innehmember having a rearward frustb-cohical portion lsp'aced inwardlylofathe -first named, frus'to-iconical portion and a forward frus'to-conical portion connected in spaced -relation to said rearward frusto .conical portion to extend ;into said diffuser .for directing primary combustion air into the combustionlchamber inwardly of said first named r frustoeconical portion, said rearward 'frust'o-conical por- 1 tion. creating turbulence immediately aft: thereof, means forintroducingl fuel into said casing, and ,'mean s for initially igniting the fuel, said flameholder stabilizing the Ucombustionof said fuel in said combustion chamber and holding. the flame of ignited fueliimmediately aft of said .first named and rearward frusto-conical por tions.

.3. .The jet engine. set forth'in claim -2, wherein swirl ,VZIIQS are disposed between said .outer and inner flameholder members for increasing the turbulence inthe .Iprimary combustion air. i

14. -A jet engine including a casing having a combustion chamber; a diifuser disposed within said casing, and a flameholder disposed inpa'rt in said diffuser, said' ijlarneholder comprising an outer member having a f rustoiconical portion and a cylindrical flange at the small end of said frusto-Iconical' portion, an inner member-having V spaced forward and rearward frusto-conical portions.and

a cylindrical portion connecting said spaced frusto-conical .rportions vancL.swirlflyanesaconnectedmbetweenasaid"cylindrical flange of the outer member and said cylindrical portion of said inner member between said spaced frustoconical portions 5. The jet engine set forth in claim 4, wherein said swirl vanes are circumierentially spaced about said cylindrical portion and are radially directed for holding said inner aiid' outer mein'b'eis inlcsneairibsalaries. 7

1 6. I-he jet, engi ne set forth in clai m g wherein said irmerfland outeif berslare maintained in iic "riaa'on with said frusto-conical brim membersurrounding said rearward frust -comcal portion of said inner member.

7. A jet engine inc ludinga casir gt haying a combustion chamber, a diifuser disposed wit hin said casing, and a flameholder disposed in part in said diffuser, said flameholder comprising: an outer member having a frusto conical portion witht a' cylindrical portion at its smaller end; an inner member -having a rearward -fri1sto-coni cal portion partly overlapped by said frusto-conical portion of said'.outermember, a cylindricalportion-connected with the smaller end of said rearward -frus to-co n-ial-portion and extending through said cylindrical portion of "said 7 outer meniber, and-a forward frusto-conical portion haying its larger end connected with said second named a cylindrical portion; and swirl vanes radially; directedand interconnecting said cylindrical portions 0f said inner and outer members.

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